A simple protein antigen bovine serum albumin (BSA) has been chemically altered by conjugation with dodecanoic acid (D-BSA) and dodecylamine (DA-BSA). These lipid coupled antigens have a somewhat better capacity to induce delayed hypersensitivity than unaltered BSA. The DA-BSA in particular sticks tenaciously to cells and persists at sites of injection for long periods. Coupling of lipid moieties to ABA-tyrosine results in a simple molecule which however still requires macrophages for initiation of in vitro stimulation of ABA-sensitive lymphocytes. The lipid complex however is highly efficient for pulsing macrophages because of its membrane adherent properties. T-cell mediated cytotoxicity to the ABA determinant has not yet been achieved in guinea pigs. We are continuing to explore the role of Ia and MHC antigens in this phenomenon.